Electronic musical instruments



M. DAVIS ELECTRONIC MUSICAL INSTRUMENTS- Aug. '25, 1959 9 Sheets-Sheet 1Original Filed June 6, 1947 FIG I CLAMPING CIRCUIT AMPLIFYING SWEEPCIRCUIT LIMIT CONTROL CIRCUITS SWEEP ATTENUATOR AMPLIFIER CIRCUITSINVENTOR MERLIN DAVIS BY m AEENT Aug. 25, 1959 M. DAVIS 2,900,861

ELECTRONIC MUSICAL INSTRUMENTS Original Filed June 6, 1947 9Sheets-Sheet 2 65 IOI IOI' 56 Ill FIG 3 INI'ENTOR.

MERLIN DAVIS BY Moi/54.,

AGENT Aug. 25; 1959 'M. DAVIS 2,900,361

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ELECTRONIC MUSICAL INSTRUMENTS Original Filed June 6, 1947 9Sheets-Sheet 8 7-: HARMONIC FIG I3 COMPENSATION 493 AND ATTENUATION 49a49| PULSE I] INTEGRATOR 25% #194 DETECTOR 244 I AMPLIFIER 27s PEAKER 509I HORIZONTAL VERTICAL SWEEP SWEEP RAD'AL CIRCUIT CIRCUIT SAW TOOTHOSCILLATOR 50s 502 SINE WAVE -5o3 OSCILLATOR DISTRIBUTOR ,soI FREQUENCYCONTROL \J INVENTOR MERLIN DAVIS BY Mona AG ENT Aug. 25, 1959 M. DAVIS2,900,861

ELECTRONIC MUSICAL INSTRUMENTS Original Filed June 6, 1947 9Sheets-Sheet 9 FIG I4 FIG I5 536 40 ATTENUATOR CIRCUITS .443 42AMPLIFIER 1 43 SWEEP CIRCUIT 546 OSCILLATOR FIG I? 56. FIG :8

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FIG l6 565 INTEGRATOR ATTENUATOR s AND CIRCUITS DETECTOR 6 CIRCUITS U EJ /7 INTEG ATTENUATOQ l/J INVENTOR AND MERLIN DAVIS DETECTOR CIRCUITS BY.2, g

576 AGENT United States Patent ELECTRONIC MUSICAL INSTRUMENTS MerlinDavis, Washington, D.C.

Original application June 6, 1947, Serial No. 753,118,

now Patent No. 2,601,265, dated June 24, 1952. Divided and thisapplication May 15, 1952, Serial No. 288,068

17 Claims. (Cl. 84-1.28) (Granted under Title 35, US. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States for governmental purposeswithout the payment to me of any royalty thereon in accordance with theprovisions of the act of April 30, 1928 (ch. 460, 45 Stat. L. 467).

This invention relates to an electronic musical instrument and morespecifically to an electronic instrument for the production of complexsounds. This application is a division of my copending application,Serial No. 753,118, filed June 6, 1947, which issued on June 24, 1952,as U.S. Patent No. 2,601,265.

Each individual musical note has pitch, quality, and intensity. Thepitch is determined by its frequency or by the number of vibrations persecond it causes in the air. This characteristic determines Whether anote is high or low. The quality of the note depends upon whether it isheard as a pure sine wave containing only one frequency or whether it isa compound wave containing a dominant fundamental frequency along withone or more harmonics or multiples of the fundamental. Quality is thecharacteristic which allows distinction between notes of the same pitchproduced by different instruments. Intensity is a measure of theamplitude of the sound wave and is the characteristic which determinesloudness. Control of the intensity of a note or of any part ofarendition is known as dynamic control.

Musical notes as sounded by instruments also have a distinguishingcharacteristic in the variation of intensity with respect to the time ofduration of the note. In some instruments such as the organ each note isof substantially uniform intensity as long as the keyboard lever is helddown. In other instruments, such as those in which a string is struck orplucked, the intensity may with more or less rapidity build up to amaximum and die away with moreor less slowness. The increase of volumeduring the initial part of the note is known as the attack and thedecrease in intensity as the note dies away is known as the decay. Thischaracteristic also provides a distinction between notes of the samepitch of dilferent instruments.

Some instruments such as the piano and organ permit the sounding of aplurality of notes simultaneously to produce harmony. Two or more notesthus played at once produce a chord. If the ratio between thefrequencies of the notes in a chord has a low value, beat notes of slowfrequency are produced and such chords are pleasing to the ear and aresaid to be consonant. However, if the beat notes produced have arelatively high frequency the sound is displeasing to the ear and thechord is said to be dissonant.

The diatonic scale used in modern music has eight notes or steps in anoctave, if the last note, one octave higher than the first note, iscounted. The octave appears to the ear as a truly natural interval, anote being of twice the frequency of a note an octave lower. In thediatonic scale the intervals between notes have been selected to obtainthe maximum of consonance when the notes are sounded simultaneously inchords. The succession of intervals between notes in the diatonicsuccession is as follows: tone-tone-semitone-tone-tone-tone-semitone.

The modes or arrangements of succession of the diatonic scale as usedtoday are the major and minor. in the major mode the arrangement is asgiven above. In one minor mode the same succession of intervals isarranged as follows: tone-semitone-tone-tone-semitone-tonetone.

In the application of the diatonic scale it is natural to select thelowest note of which the scale is composed as the key-note. In music thekey-note is invested with special significance making the other sixsubservient to it. In the scale of C major the lowest note is C and thearrangement of intervals up the scale must be as outlined above for themajor mode. Music is written with 12 diiferent keynotes and, because thediatonic scale intervals are more or less incommensurate, it is foundthat each of these keys requires a different keyboard on a musicalinstrument for exact intonation.

To avoid either twelve keyboards or fifty keyboard levers per octave aswould be necessary to accurately render music in both modes and in thevarious keys, a compromise is customarily made in musical instruments byproviding in each octave twelve notes the spaces between which areequally proportioned. Such an arrangement is known as equal temperamentand provides a close approximation for each of the keys. The scalehaving 12 notes per octave, the notes being approximately a half-toneapart is known as the chromatic scale. This arrangement does not allowaccurate rendition of each key since the sharp of one note is not, as sooften supposed, the same as the flat of the note following. Aninstrument arranged for accurate tonal rendition of a key is said tohave just temperament.

It is an object of this invention to produce a musical instnlment inwhich a plurality of dilferently pitched notes may be producedsuccessively by a single means for producing oscillations.

It is also an object to provide a musical instrument in which a complexsound may be produced appearing to the car as a chord composed ofseveral notes of diiferent pitch being sounded simultaneously, saidcomplex sound being produced by a single means for producingoscillations.

It is also an object to provide a musical instrument in which a singlekeyboard in cooperation with a single oscillation producing means willproduce a chord appearing to the ear to consist of thirteen notes of thechromatic scale sounded simultaneously, two of which notes are separatedby an octave.

It is also an object to provide a musical instrument which may be simplyadjusted to play either in just or equal temperament.

It is also an object to provide a musical instrument which may be simplyand selectively adjusted to play in any of a plurality of modes and inany of a plurality of keys so that the keyboard may always bemanipulated in one desired key while the music is produced in a keycorresponding to the adjustment.

It is also an object of this invention to provide a musical instrumentwherein the quality of the notes produced may be generally adjusted.

It is also an object to provide a musical instrument wherein the qualityof each note may be separately adjusted to vary with respect to time ofduration of the note.

It is also an object to provide a musical instrument in which theintensity of each note may be controlled by the pressure exerted on thecorresponding keyboard lever.

It is also an object of this invention to provide a musical instrumentin which the intensity of each note may be varied in predeterminedmanner with respect to the time of duration of said note.

It is also an object of this invention to provide a musical instrumentin which a main keyboard representing the notes of the chromatic scaleis provided with a supplementary keyboard whereby operation of a key onsaid supplementary keyboard will sound a corresponding note andsimultaneously a note one octave higher or lower.

Other objects will become apparent from the following description takenin connection with the drawings in which:

Fig. 1 is a schematic diagram of one embodiment of this invention.

Fig. 2 shows a 2manual keyboard to be used with this invention.

Fig. 2a shows a detail of part of the tremolo producing means.

Fig. 3 is a detailed cross-sectional perspective view of one keyboardmanual.

Fig. 4 is a simplified block diagram of one embodiment of thisinvention.

Figs. 5a to 5] are curves used in explaining the operation of Fig. 4.

Fig. 6 is a schematic diagram of one embodiment of this invention.

Fig. 7 is a schematic diagram showing one system of dynamic control thatmay be used with this invention.

Fig. 8 is a schematic diagram showing a portion of the volume controlused with this invention.

Fig. 9 is a schematic diagram showing one system of quality control thatmay be used with this invention.

Fig. 10 is a schematic diagram of an alternative system of qualitycontrol.

Fig. 11 is an alternate electronic distributor device that may be usedwith this invention.

Fig. 12 is a block diagram of an embodiment of this invention usingconcentric wave patterns.

Fig. 13 is an elevation view of the wave patterns used in the embodimentof Fig. 12.

Fig. 14 is a partial block diagram showing an embodiment of thisinvention using cylindrical wave patterns.

Fig. 15 is a partial block diagram showing other elements of the systemof Fig. 14.

Fig. 16 is a block diagram of an embodiment of this invention usingcomplementary wave patterns connected in push-pull relation.

Fig. 17 is an elevation view of the push-pull patterns used in thesystem of Fig. 16.

Fig. 18 is a sectional side view of the patterns shown in Fig. 17.

Reference is now made more particularly to Fig. 1 of the drawing inwhich cathode ray tube 34) has an electron gun 31 for producing anelectron beam. Tube 30 is so arranged that the beam has the shape of aribbon having a comparatively long vertical dimension and a shorthorizontal dimension, the cross section of the beam as it impinges onthe end wall 32 being substantially a line as shown at 33. Deflectingplates 34 are provided for de fleeting said beam horizontally. End wall32 carries a plurality of patterns 36, 37, and 38 which may varysinusoidally in form and which may be made of metal foil. The uppermostpattern 36 consists of one complete sine wave. The second pattern 37while of substantially the same length as pattern 36, consists of twosine waves. Pattern 38 which is of the same length consists of threesine waves. It will thus be seen that pattern 37 represents a wave whichis the second harmonic of wave 36 while pattern 38 represents a wavewhich is the third harmonic of pattern 36. Patterns 36, 37, and 38 areconnected through attenuator circuits 4%, which are controlled by stops41, and through amplifier 42 which is in turn connected to speaker 43.Attenuator circuit 40 is constructed to selectively attenuate thesignals picked up by patterns 36-38 as will be disclosed in greaterdetail below.

Electrode 44, also carried by end wall 32 of tube 30, is located inalignment with one end of the patterns 3638. Electrode 44 is connectedthrough conductor 45 to sweep-limit control circuit 46. A circuitsuitable as a sweep limit control circuit will be described in detailwith respect to Fig. 6. Deflecting plates 34 are connected throughclamping circuit 47 and amplifying circuit 48 to saw-tooth oscillatorcircuit 50.

Saw-tooth oscillator circuit 50 comprises a condenser 51 connected inparallel with a gas-filled triode 52. The cathode of vacuum tube 52 isconnected to ground. The grid of tube 52 is connected to ground througha biasing battery 53, and is inductively coupled through coils 55 and 56to sweep-limit control circuit 46. The plate of tube 52 is connectedthrough frequency control pentode 60 to plus battery and through thebattery to ground completing the circuit for charging condenser 51through pentode 6d. Condenser 51 is discharged through triode 52. Thecathode of tube 60 is connected to the plate of tube 52 and the plate oftube 60 is connected to plus battery.

A keyboard 65 is provided along with a supplementary keyboard 66.Keyboard 65 comprises the usual black and white levers of the piano ororgan as will be described in greater detail below. Keyboard 66 consistsof very short levers, one corresponding to each of the black and whitelevers on keyboard 65, each keyboard lever in keyboard 66 being directlyin front of and closely adjacent to the corresponding lever in keyboard65. Each lever in keyboard 65 and 66 is provided with a contact shown at67. In their normal unoperated position, these contacts engage one endof resistors 68 or 68 shown on the right side of the contacts 67. Whenthe levers are pressed, contacts 67 engage one end of resistors 69 or 69shown on the left side of contacts 67. The other ends of resistors 68and 69 are connected together and through battery 72 to the cathode 73of cathode ray tube 75.

Thirteen electrodes such as shown at 81-93 are fixed to the end wall oftube 75. Tube 75 is also provided with deflecting plates '76 and 77 fordeflecting the cathode ray beam in mutually perpendicular directions,the oathode ray beam being produced by electron gun 78. Deflectingplates 76 and 77 are supplied by sweep circuits 74 with sine wavesdegrees out of phase so that the electron beam is swept in a continuouscircle over electrodes 81-93 at a super-audible speed. Twelve of theseelectrodes 81-93 are each connected to one of the contacts 67 in eachoctave of the normal keyboard 65 through conductors such as and 96. Thethirteenth electrode 93 is connected to contacts 67 of the supplementarykeyboard 66.

One keyboard lever 70 of keyboard 66 has associated therewith resistors68' and 69' corresponding to resistors 68 and 69 of keyboard 65.Keyboard lever 70 controls a contact 67 which engages one end ofresistor 68 when the lever is unoperated and one end of resistor 69 whenthe lever is pressed. However, the other levers of keyboard 66 haveassociated therewith a contact 71 which is connected to the end of saidresistor 68 which engages contact 67 associated with lever 70. The otherends of resistors 68, 68, 69, and 69 are connected to battery 72 andalso to the cathode of pentode 60. The contacts such as 71 in connectionwith keyboard 66 may be used in place of the plurality of resistors 68as shown in connection with keyboard 65 because only one lever oikeyboard 66 is ever depressed at one time whereas a plurality of leverson keyboard 65 are operated simultaneously therefore one silent resistorwill serve the entire keyboard 66.

Resistors 68, 68, 69 and 69 are successively connected in a circuitincluding battery 72, the electron beam of tube 75 and one of contacts81-93. Connections are made from the other ends of resistors 68 and 68and selected points on resistors 69 and 69 to the grid of tube 68.Resistors 68, 68', 69 and 69 therefore form parts of potentiometers andthe voltage picked up across resistors 68 and 68 is sufficient toprevent tube 60 from passing current while the voltage picked up fromthe intermediate taps of resistors 69 and 69 causes tube 60 to pressedon keyboards 65 and 66.

the charging rate of condenser 51.

pass current commensurate with the board lever pressed.

The selected points of resistors 69 mentioned above are shifted slightlyalong said resistors through the action of switches 97. There is oneswitch 97 provided for each resistor 69. Switches 97 are ganged forgroup action and are operated by a single operating handle or stop 98marked just-equal? Switches 97 are effective to connect either of twoselected points to the grid of tube 60. Changing the point at which aresistor 69 is connected to the grid of tube 60 obviously will changethe pitch sounded by the associated keyboard lever. The points onresistors 69 tapped by switches 97 are so selected that with stop 98 inone position the instrument will play in just temperament and with thestop 98 in the other position the instrument will play in equaltemperament. Switches, not shown, similar to switches 97 should beprovided for resistors 69' of keyboard 66.

In just temperament a change in the key note from one note to the nexthigher note means that the pitch of all the notes is raised by beingmultiplied by the pitch ratio of said two key notes. In just temperamentthis pitch ratio between adjacent notes will not be the same for everytwo adjacent notes. In equal temperament a change from one key note tothe next higher key note means that the pitch of all notes is raised bybeing multiplied by 1,059, a number such that its product and succeedingproducts will divide an octave into twelve equal intervals. In equaltemperament since all the notes are raised by one factor when the keynote is changed the key signature stop may operate one set of switchesadjusting the resistance of one resistor in the connection betweencathode 73 of distributor 75 and keyboards 65 and 66.

In operation, when levers of keyboard 65 are unoperated the contacts 67engage resistors 68 but when the levers are depressed the contacts 67engage resistors 69.

tone of the key- Current flows from battery 72 through one or the otherof resistors 68 or 69 thence through whichever one of the electrodes 81to 93 on which the beam generated by electron gun 78 is impinging, andback to battery 72. Resistors 68 and '69 thus operate as potentiometersand a voltage will be applied through line 80 to the control grid ofpentode 60, said voltage being determined by the position of theintermediate tap of the resistor 69 or the voltage across resistor 68which are associated with the lever pressed. Supplementary keyboard 66operates in a similar manner current passing through electrode 93 andthrough whichever resistor 69 that corresponds to the lever pressed.However, when a lever is pressed on keyboard 66 the corresponding leveris also operated in keyboard 65 because of a mechanical linkage, to bedescribed more in detail later, between the levers of keyboard 66 and65. This arrangement allows two notes one octave apart in pitch to besounded simultaneously on one keyboard.

Various voltages are thus applied in quick succession to the controlgrid of tube 60, these voltages correspond ing in magnitude to the pitchrepresented by the levers The current through tube '60 varies inaccordance with the voltage on its control grid and charges condenser 51at varying rates of speed. Condenser 51 is discharged by triode 52. Uponactuation by the impinging of the electron beam in tube 30 on electrode44 sweep-limit control circuit 46 applies a pulse to the grid of triode52 through inductively coupled coils 55-5'6 to cause tube 52 to conduct.This causes condenser 51 to discharge as trace 33 completes its sweepover patterns 36-38 and causes trace 33 to return to the beginning ofits sweep.

The voltage to which condenser 51 is charged is amplified by circuit 48and converted into two oppositely swinging voltages each of which swingsin a direction opposite to the other and at a rate in accordance withThese oppositely 'swiiigihg voltages are applied to clamping circuit 47which fixes the upper limit of the swing of each of the voltages andapplies them to the deflecting plates 34 of tube 30 to limit the travelwithin the bounds of the patterns on the side opposite electrode 44.This causes the ribbon beam of tube 30 to swing back and forth acrosspatterns 36, 37 and 38. At any instant more or less current will flowfrom patterns 3638 in accordance with the area of said patterns that isbeing impinged upon at that instant by the electron beam. Thus it willbe seen that the current will flow representing the fundamental inaccordance with pattern 36 and also the harmonics represented bypatterns 37 and 38. The current picked up by patterns 36+38 isattenuated in circuits 40, as controlled by stops 41, is amplified incircuit 42 and reproduced audibly by speaker 43.

If no levers on keyboards 65 or 66 are pressed the control grid of tube60 is so biased that condenser 51 is not being charged. Hence, theribbon beam in tube 30 is not deflected. A steady current will be passedon to circuit 40 and no vibrations will be audibly reproduced by speaker43. It will be obvious that the sound could also be ex; tinguished byblocking the beam in cathode ray tube 30 and that the sound could bemufiled by partially blocking said beam.

If one lever is pressed on keyboard 65, on each instant that theelectron beam of tube 75 passes the corresponding electrode ofelectrodes 81-93 condenser 51 will be charged at a rate determined bythe pitch value of the key pressed. During this instant the ribbon beamin tube 30 will move horizontally along the patterns generating acurrent having a fundamental and harmonics at a frequency depending onthe pitch value of the lever pressed. A corresponding operation willfollow from the pressing of the other levers in keyboard 65.

If two levers are simultaneously pressed on keyboard 65, the pitch ofone lever will be sounded as the electron beam in tube 75 impinges onits corresponding electrode of electrodes 81 to 93 while the pitch ofthe other key will be sounded as its corresponding electrode is impingedupon. The rate of sweep of the electron beam in tube 75 is at asuperaudible rate so that the pitches of the two notes are heard insuccession during very small increments of time. It will then appear tothe ear that the two notes are played simultaneously. It will be evidentthat all twelve notes in the chromatic scale may be sounded at one time,the notes being scattered throughout the octaves on the keyboard.

If two notes an octave apart are to be sounded simultaneously then thelever on the supplementary keyboard 66 corresponding to the lower of thetwo notes, for right hand execution or higher of the two notes for lefthand use is pressed. This action automatically presses the leveropposite and corresponding to the upper or lower octave note in keyboard65 and it is sounded through the action described above. The pitchresistors 69' are arranged so that the levers of keyboard 66 to theright of the center sound a note one octave lower than the opposinglever on keyboard 65 while the levers of keyboard 66 to the left of thecenter sound a note one octave higher than the opposing lever ofkeyboard 65. The lever of keyboard 66 which is pressed contacts aresistor 69' and causes a current to flow by impingement of the beam onelectrode 93 of tube 75 causing the note an octave higher to be soundedduring the thirteenth increment of the sweep-cycle in tube 75.

It is thus seen that, through the operation of a single oscillationproducing means 30, a plurality of pitches may be produced in successionand that these pitches can be produced in such rapid succession thatthey appear to the ear to be simultaneously sounded.

In Fig. 2 is shown the two-manual keyboard arrangement preferably usedin this invention. The two main keyboards 65 and 65' are each associatedwith auxiliary octave keyboards 66 and 66', respectively. The means forproducing a tremolo effect are mounted immediately behind the keyboardsand will be described, in detail below.

The construction of a main keyboard 65 and octave keyboard 66 is shownin Fig. 3. White lever 100 and black lever 101 of keyboard 65 correspondto the black and White levers on the keyboard of a conventional piano.Levers 100' and 101 of octave keyboard 66 are directly in front ofcorresponding levers 100 and 101. Lever 100 is provided with a hinge at102 and maintained in its normal up position by tension spring 103.Lever 100 is provided with a hinge 106 and maintained in its normal upposition by adjustable compression spring 107. Adjustable dashpots 109and 110 provide a proper inertia to the action of levers 100 and 100,respectively. The other levers of keyboard 65 and 66 are similarlyprovided with hinges, springs and dashpots, and have a similarconstruction. Hook member 111 fixed to lever 100 cooperating with member112 of lever 100 causes lever 100 to be depressed when octave lever 100is pressed.

If two notes one octave apart are to be played, the lever of octavekeyboard 66 adjacent to the lower note in right hand execution (oradjacent to the upper note for left hand execution) on keyboard 65 ispressed. The operating of the octave lever also operates the lever ofkeyboard 65. Thus without unduly stretching the fingers, a note, alongwith a note an octave higher or lower, as required is sounded byoperation of one keyboard lever. The electrical contacts necessarilyassociated with the levers of keyboards 65 and 66 are not shown in Fig.3.

Referring now more particularly to Fig. 4 for a general description of amodification of this invention, cathode ray tube 115 is of the typewhich produces a pencillike beam of narrow cross-section. Tube 115includes cathode 116, horizontal deflecting plate 117, verticaldeflecting plates 118 and patterns 1 19 and 120.

Horizontal deflecting plates 117 are connected by leads 117a tohorizontal sweep circuit 122 which is in turn controlled by keyboard123. It will be understood that keyboard 123 and horizontal sweepcircuit 122 have associated therewith an octave keyboard and distributoras shown in Fig. 1. Vertical deflecting plates 118 are connected byleads 118a to vertical sweep circuit 124.

Patterns 119 and 120 are connected through frequency compensator circuit126 and harmonics attenuator circuit 127, coupling circuit 128 to pulseintegrator circuit 129. Circuit 126 contains a pre-set resistor for eachof patterns 119 and 120, the resistor attenuating the signal picked upby each pattern to compensate for the selective hearing characteristicsof the ear. Circuit 127 provides for the circuit of each of patterns 119and 120 a potentiometer including a tapered resistance. Thesepotentiometers are selectively operable by stops not shown so that thevarious harmonics can be suppressed or accentuated in order to simulatediiferent musical instruments or produce new complex sounds.

Coupling circuit 128' gives a direct current coupling between harmonicsattenuator 127 and pulse integrator 129. Pulse integrator 129 is acircuit capable of integrating the electrical pulses supplied to itduring each vertical sweep of the electron beam in cathode ray tube 115.Conductor 130 connects vertical sweep circuit 124 with pulse integrator129 to supply the latter with a tripping pulse at the end of eachvertical sweep. Pulse integrator circuit 129 is connected throughdetector 135 and amplifier 136 to speaker 137. Circuits 128, 129, 135,and 136 will be described in greater detail below.

In the operation of the system shown in Fig. 4, the spot trace of thepencil electron beam produced in tube 115 sweeps vertically overpatterns 119 and 120 at a relatively rapid rate determined by sweepcircuit 124. The pencil beam of tube 115 sweeps across patterns 119-120horizontally at a rate which depends on the lever being operated inkeyboard 123 but at a rate which is always slow compared to the verticalsweep rate.

In Fig. a there are representations of fundamental pattern 119 andsecond harmonic pattern 120 with line 140 representing the trace of spot140' of the pencil beam. Arrows indicate components of beam travel.Although shown vertical the beam trace would have a slight slope as itproceeds in zigzag fashion across the patterns. The return trace of thebeam is ignored because it is so rapid as to produce a negligiblesignal. If desired the return trace may be blanked out by use of ablanking pulse applied to a control grid in cathode ray tube 115. Fig.5b shows the signal produced by the patterns 119120, neglecting theeffects of frequency discrimination compensator circuit 126 which wouldgovern the relative amplitude of the signals emanating from the patternsin accordance with auditory requirements. In Fig. 5b the unshaded andshaded pulses represent the signal produced by transit of the beamacross patterns 119 and respectively along representative traces 140"shown in Fig. 5a. It will be obvious that as the beam traverses thepatterns in a nearly vertical direction there will be produced by eachpatteln a pulse having a duration equal to the time during which thebeam impinged on the pattern, and since the vertical deflection rate isuniform, the pulse duration will be a measure of the pattern height atthe position of that trace.

Fig. 5c shows the pulses produced by patterns 119 and 120 afterattenuation by compensating network 126 and harmonics attenuator 127. Inthis figure the pulses representing the second harmonic have beenappreciably attenuated either to compensate for the selectivecharacteristics of the ear or because of selective suppression of thisharmonic to achieve a desired effect, or for both reasons.

Fig. 5d shows the output of pulse integrator 129 in which a condenser ischarged as shown in Fig. 5 by the pulses shown in Fig. 5c. Fig. 5 showsthe condenser charge voltage plotted against time. The higher thevoltage of the pulse, the higher will be the charging rate of thecondenser, curves CR -CR showing different charging rates. As seen inFig. 5d, the condenser will be charged at a high rate (angle A) for ahigh pulse and at a slow rate (angle B) for a short pulse and will bedischarged at the end of each complete vertical sweep through action oftie between pulse integrator circuit 129 and vertical sweep circuit 124.

Detector detects the pulses produced by integrator circuit 129 andproduces a curve such as shown in Fig. 52, it being understood that inpractice there would be a large number of integrated pulses as shown inFig. 5d to give a relatively smooth curve as shown in Fig. 5c. The speedwith which the electron beam in tube 115 is deflected horizontallydepends on the lever pressed on keyboard 123. This rate of horizontaldeflection determines the length in time of the wave shown in Fig. 5ewhich, in turn, determines the pitch of the note sounded.

Reference is now made to Fig. 6 for a detailed description of anembodiment of this invention operating with a pencil cathode ray beam asgenerally described with respect to Figs. 4 and Sa-Sf. Cathode ray tubeincludes cathode 151, control grid 152, horizontal deflecting plates153, vertical deflecting plates 154 and on its end wall there is amounting plate 155 carrying patterns 156-165. Power supply providesvoltages to the various electrodes of tube 150 to produce a pencil beamof relatively small cross section.

In Fig. 6 the conductors 95, 96, etc. corresponding to the conductors oflike number in Fig. 1 lead to the contacts of the distributor tubethrough resistors 171, 172, etc. Resistors 171 and 172 are arranged withshorting switches 173 and 174, respectively, arranged to selectivelyshunt parts of said resistors. Shorting switches 173, 174 are ganged tooperate from key signature stops 175 and 176, each stop operating oneshorting switch of each resistor. It will be understood that the wiresassociated with each keyboard lever each contain a potentiometer like68, 68, 69, 69' of Fig. I. The resistors 171 and 172 lead to thecontacts 131 of a distributor tube 182. This distributor tubecorresponds to distributor tube 75 in Fig. 1. Tube 182, however, is analternate type being a cylindrical tube having its contacts 181 incylindrical array and the cathode 183 running axially of the tube.Deflection coils 185, 186, 187 and 188 are fed with an alternatingcurrent from source 190. Condenser 191 is connected in series with coil186 so that a rotating field will be produced about tube 182 and cause aplanar sheet of electrons to be emitted from cathode 183 and sweepradially around the tube and across the contacts 181 at a speeddetermined by the frequency of the source 190.

The anodes 181 of distributor tube 182 may be separated andshielded fromeach other to prevent the beam from impinging on two anodes at the sametime. The resistance of the beam contact as it passes from one anode 181to the next is so low in comparison to the impedance in series with itthat the effect should not be apparent until the beam has almost passedover one anode prior to contact with the next. I The switching speed ofthe electronic distributor tube 182 of Fig. '6 is limited only by themagnetic properties of the rotary sweep circuit and this may be as highas 10,000 cycles per second which would allow 130,000 switchings persecond. Switching from one audible frequency to another is performed ata supersonic rate.

Resistors such as 171 and 172 appearing in the potentiometer circuitassociated with each keyboard lever will obviously affect the currentpassing through these potentiomete'r circuits in accordance with theamount of the resistances 171, 172, etc. that are shorted out by the keysignature stops such as 175 and 176. amount of shorting in turn willaffect the voltage applied to the grid of tube 60 through conductor 79and thus affect the pitch of the note sounded. Shorting switches such asthose designated as 173 are positioned along resistor 171 so thatoperation of one key signature stop such as 175 operating to close oneshorting switch in each resistor 171, 172, etc. will cause the notessounded by keyboards 65 and 66 to be in any one of the various keys andmodes represented by stops 175 and 176. Other stops arranged in equalmanner may be employed to provide alternate potentiometer taps to causethe instrument to play in equal or just temperament and in the variousmodes. I

The switches such as 173 may be arranged so that the over-all pitchlever is raised by the resistors such as 171 until the base frequency orpitch sounded by the white keyboard lever normally producing C-naturalis equal to that of the key note represented by the signature. The whitekeys which normally represent the scale at the key of C now willrepresent the scale in the key selected. The signature written on themusic will remain as usual but the musical notation will need to betransposed to the key of C. In this system, except for transposingaccidentals, all music will be played on the white keyboard levers andthe given note position on the staflf will always be represented by thesame keyboard lever. Each keyboard lever will therefore sound adifferent pitch depending upon the key selected in contrast with pianooperation in which each keyboard lever always sounds the same pitch. Ifthe scale pitches are selected in the just tempered scale then trueharmony will result. Adjustment from equal to just temperament or viceversa is affected by gang selector switches operating on the pitchpotentiometer such as switches 97 in Fig. 1. In order to play in thevarious minor as well as the major modes from 12 to 26 key signaturechange switches will be required. Since the minor mode scale steparrangement difiers from the major mode, additional gang selectorswitches such as 173 in Fig. 6 operating on the pitch potential circuitwill be required. The black keyboard levers would then be arranged torepresent intermediate frequencies between key scale steps formodulation purposes. These might have equal tempered values or justtemperament attuning to selected transposition keys.

Alternatively, the switches such as 173 in Fig. 6 may be arranged sothat music written in keys other than the key of C (Le. written insharps or flats) may be played on the keyboard as though written in thekey of C. In this system the musical notation would be used unmodified.The keyboard would be played as usual except that the key signatureflats and sharps would be disregarded and executed as though natural.The shift of the white keys to the proper sharps and flats would be doneby depressing key signature switches such as 173 in Fig. 6. In thissystem all of the notes are not shifted by a certain ratio but thevarious notes are changed in pitch each by its required amount. X

Wire 79 from keyboards 65 and 66 is connected with the control grid ofpentode 60. The cathode of pentode 60 is connected to conductor 80 fromkeyboards 65 and 66. Frequency control tube 60 is connected to saw-toothoscillator circuit 50 as explained with respect to Fig. 1. The output ofsaw-tooth oscillator circuit 50 is fed to paraphase amplifier circuit 48containing triodes and 196. The plate of gas-filled tube 52 is connectedthrough condenser 197 to the grid of tube 195. The junction of condenser197 and the grid of tube 195 is connected through resistors 198 and 199to the cathodes of tubes 195 and 196. The junction of resistors 198 and199 is connected to the grid of tube 196.

The particular form of par'aphase amplifier employed in circuit 48employs coupling between the cathodes of the two tubes 195 and 196.Current from both tubes flows through the common cathode resistor 199.Grid voltage on tube 196 is the voltage developed across cathoderesistor 199 and is of opposite sense to that directly on the of theamplifying tube 195. The output of triode 1 96 is thus invented withrespect to the output of tube 195. The plates of triodes 195 and 196 areeach connected through a separate resistor to a common source of pluspotential. The outputs of paraphase amplifier 48, two mutually invertedsaw-tooth waves, are fed to clamp ing circuit 47. I

Clamping circuit 47 comprises diodes 200 and 201. The output of triode195 is connected to the cathode of tube 201 and also to one of thehorizontal deflecting plates 153 of cathode ray tube 150. The output oftriode 196 is connected to the plate of diode 200 and also to the otherof deflecting plates 153. The plate of diode 201 is connected to groundwhile the cathode of diode 200 is connected to an adjustable biasingsource of potential. It will be obvious that diodes 200 and 201 willconduct in opposite directions when the mutually inverted deflectionvoltages attain suflicient amplitude. This results in clamping oneextreme of each opposed saw-toothed horizontal deflecting voltage at onepoint and causes one side of the sweep of the electron beam to remainalways fixed regardless of amplitude variations.

The vertical deflection voltage is initiated in saw-tooth oscillator205, a vacuum tube oscillator capable of generating a frequency of100,000 cycles per second or more. Oscillator circuit 205 comprisestriode 206 and pentode 207. The potential of [the cathode of triode 206is maintained above ground by cathode resistor 208. The grid of tube 206can be made highly negative with respect to its cathode since it isdependent upon the current through pentode 207. The current throughpentode 207 may be regulated by adjustment of its screen grid voltagethrough manipulation of potentiometer 209. Triode 206 will benon-conducting while condenser 211 is being charged from source of pluspotential 212. As condenser 2111 becomes charged triode 206 becomesconducting regardless of the highly negative grid. This results in platecurrent through resistor 213. The grid of pentode 207 is therebyaifected through condenser 214 and resistor 215. The grid of pentode 207then goes negative and current decreases through pentode 207. Because ofthe grid connection of triode 206 with plate resistor 2'16 triode 206becomes more conducting and finally positive. Condenser 211 dischargesvery quickly through this tube. When voltage across condenser 211decreases enough the grid of triode 206 gains control and the cyclerepeats.

The output of oscillation generator 205, a saw tooth wave, is fed to theinput of paraphase amplifier 220 through the primary of transformer 221.The secondary of transformer 221 operates to trip the pulse integratorin a manner to be described later. Paraphase amplifier 220 has aconstruction and operation similar to that already described forparaphase amplifier 48. The output from paraphase amplifier 220 isconnected through clamping circuit 222 to vertical deflecting plates 154of cathode ray tube 150. The construction and operation of clampingcircuit 222 is similar to that described above with respect to clampingcircuit 47.

In tube 150 each of patterns 156 to 165 are connected through frequencycompensating resistors such as 225 to tapered harmonic-attenuatorresistors such as 226. Resistor 226 forms part of the potentiometercircuit going back to voltage supply 170. The adjustable tap along eachlogarithmically tapered resistor 226 feeds through a resistor 227 to thecathode of diode 230 and the plate of diode 231 in positive couplingcircuit 233.

Frequency compensating resistors 225 correspond to the resistors incircuit 126 of Fig. 4 while the tapered potentiometers, such as 226,correspond to those in the circuit 127 of Fig. 4. The function andpurpose of circuits 126 and 127 has already been explained with respectto Fig. 4. Since the voltages from potentiometers such as 226 must becombined before being amplified for the speakers, high series resistorssuch as 227 must be added in the voltage tap line of each potentiometer226 to prevent short-circuiting when these lines are connected to acommon lead. A switch such as 232 is shown between each resistor 225 andpotentiometer 226 is provided whereby each anode 156 may be groundedwhen not used in order to prevent the anodes from accumulating a chargewhen disconnected.

The purpose of the positive coupling stage 233 is to assure that thecoupling condenser 234 used to block potentiometer voltage from the gridof the pentode 236 in pulse integrator circuit 237 is not renderedinsensitive to the incoming pulses by accumulation of charge, and toinsure that the pulsations are transmitted with their full intensity.Incoming pulses are prevented from shorting to ground by the rectifyingaction of diode 231 while passing unimpeded through diode 230. Thevoltage drop across grid resistor 238 supplies the signal pulse passedon to pulse integrator circuit 237. In this process a small chargeaccumulates on condenser 234. During the period following the pulse thecondenser becomes neutralized by a flow of current through the groundeddiode 231. This current flow has no action on the stage 237 since thedirection of this current is opposed by the other diode. The

original signals are thereby transmitted through the cou- I plingcircuit 233, without alteration by said circuit, as unidirectionalpulses to the pulse integrator stage 237.

Pulse integrator stage 237 includes pentode 236 and triode 240. Theoutput of coupling circuit 233 is applied to the grid of pentode 236 inpulse integrator circuit 237. Circuit 237 also includes condenser 241charged by battery 242 through resistor 243 and pentode 236. Resistor243 is the cathode resistor of vacuum triode 240, the grid of which isconnected through conductor 244, differen tiator circuit 246, andconductors 247 to the secondary of transformer 221 in the input ofamplifier 220. A by-pass condenser is provided across cathode resistor243. One side of condenser 241 is connected to the cathode of triode240. The other side of condenser 241 is connected to the plate of triode240. The output of integrator circuit 237 is taken from the positiveside of condenser 241.

In operation, each pulse, such as those shown in Fig. 5c, impressed onthe grid of pentode 236 causes that tube to pass a pulse of current frombattery 242 to condenser 241. Current from battery 242 flowing throughcathode resistor 243 causes triode 240 to be normally non-conductingwith a grid bias E (Fig. 5]) within the substantially linear portions ofcondenser 241 charging curves. However, the high rate of change of thevertical deflection voltage during the return stroke of the electronbeam in tube 150 causes a pulse of relatively large magnitude to beinduced in the secondary of transformer 221 and timed to dischargecondenser 241 before the voltage has reached the cut oif voltage E Thispulse is properly shaped by diiferentiator circuit 246 and applied totrip tube 240, making that tube conducting and discharging condenser241. Differentiating circuit 246 consists of a condenser and resistor inseries forming a circuit having a time constant about one-tenth that ofthe vertical oscillation cycle applied to plates 154 of tube 150. Theeffect of integrator circuit 237 is as described with respect to theintegrator circuit in Fig. 4 and with respect to Fig. 5d.

The output of pulse integrator circuit 237, which is the charge oncondenser 241, is applied to the input of detector circuit 244, beingconnected to the plate of diode 246 and the cathode of diode 247'. Arsiestor 249 and condenser 248, connected in parallel are connectedbetween the cathode of diode 246' and the palte of diode 247 Detectorcircuit 244 operates in a manner similar to that of coupling circuit 233in that it preserves the direct current component of the signal.However, condenser 248 is charged by each pulse, such as shown in Fig.5d, in the output of the integrator circuit and discharged throughresistor 249 between pulses. The output of circuit 244 taken from acrosscondenser 248 is, therefore, the envelope of the input pulses as shownin Fig. 5a.

The output of detector circuit 244 is taken from across condenser 248and applied across tapered resistor 252 in volume control circuit 253.Condenser 250 in series with resistor 251 tapped to the lower end ofresistor 252 provides overall frequency compensation. A tap adjustablealong resistor 252 applies the output of volume control circuit 253 tothe control grid of pentode 256 which acts as a driver tube to push-pullamplifier 260. Resistor 252 is logarithmically tapered to compensate forthe logarithmic sensitivity of the ear so that equal adjustments of theintermediate tap will produce equal changes in volume.

The output of amplifier circuit 260 is impressed on the input of speakerdivider circuit 270 where it is divided into high frequencies, which areimpressed on high frequency speaker 276, and low frequencies which areimpressed on low frequency speaker 277. The high and low frequencies areseparately made audible to obtain better sound effect.

Sweep limit control circuit 46 contains triode 54, the grid of which isconnected to the junction of resistor 57 and the plus side of powersupply 170. When the electron beam of tube 150 impinges on electrode 44,a current flows through said beam, electrode 44, resistor 57 and powersupply 170 to the cathode 151 of tube 150. This momentary flow ofcurrent through resistor 57 causes a pulse to be applied to the grid oftriode 54. The amplified pulse is passed through transformer 58 to tripgas filled triode 52, as explained above, and cause the return of theelectron beam in tube 150 to the starting place along the horizontalaxis. The electrode 44 is the same as that shown in tube of Fig. 4.

Time beat emphasis circuit 234) receives spaced square waves fromgenerator 281 and applies them to control grid 152 of tube 150.Generator 281 develops square pulses of adjustable amplitude durationand spacing. The pulses applied by circuit 289 to grid 152 momentarilychange the intensity of the electron beam of tube and cause the musicrendered to have accentuated volume or beats at regular intervals. Thismay be arranged to give automatic accent of the notes at the end of eachmeasure so that the rhythm of the music may easily be held constant.

The electron beam in tube 150 may also be varied in 13 intensity tocontrol the attack-decay volume of each note as will be described belowwith respect to Fig. 7.

Reference is now made more particularly to Fig. 7 for a description ofsome of the volume or dynamic controls used in this invention. In Fig. 7is seen distributor tube 182, battery 72, pitch resistors 69, and keysignature resistors :173174 substantially as seen in Figs. 1 and 6. Fig.7, however, shows a modification of the pitch-potentiometer circuit inthat there are no silent resistors '68, the pentode 60 being so biasedthat, with no bias applied to its control grid, it will not con-duct andno charge will be fed to condenser 51. Pentode 60 is connected to thetaps of the various pitch potentiometers 69 by the pitch contacts suchas contact 300 of keyboard lever 301.

The above described potentiometer circuit for selective pitch control isan additional modification in that the contacts 300 and 300 break thevarious potential lines to the grid of the pentode tube 60 rather thanthe current in the various parallel potentiometer circuits. It will beunderstood that there is a contact such as 300 and 300 for each lever onthe main keyboard and that each of such contacts is associated with alever such as 301. I

In Fig. 7 the pitch potentiometer circuit associated with keyboard lever301 includes. the electron beam and a contact 181 of distributor tube182, battery 72, pitch resistor 69 and key-signature resistor 173. Inparallel with this circuit are one or more dynamic control circuitsincluding the electron beam and a contact 181 of distrib utor tube 182,battery 72, attackdecay potentiometer 304 and resistors 305. Since eachof these parallel circuits have high impedances, current drain in onecircuit does not materially affect the other.

The attack-decay potentiometer 304 includes a tapered ring-like resistor306, the inner surface of which is circular and engaged by rotatingcontactor 307. Contactor 307 is fixed to shaft 308 of motor 309. Shaft308 is normally prevented from rotating by arm 312 fixed thereto whichnormally abuts against arresting member 314 carried by bar 315. Bar 315is slidably mounted in supports 3 17 and 318 and carries arrestingmember 320 capable of arresting arm 312 after it has rotated 180 degreesfrom member 314. Bar 315 is moved in an axial direction by solenoid 322and is biased by spring 321 so that arm 312 normally abuts againstarresting member 314.

When solenoid 322 is energized, bar 315 is moved against the tension ofspring 321; arresting member 314 is moved from under arm 312 and shaft308 starts to rotate carrying with it contact 307. With the moving ofbar 315 arresting member 320 has now of arm 312 and arrests arm 312after it has rotated 180 degrees. When solenoid 322 is deenergized, bar315 moves to its normal position, arresting member 320 is moved fromover arm 312 and shaft 308 and contact 307 rotate another 180 degreestill arm 312 is again arrested by member 314. Solenoid 322 is connectedin series with battery 334, adjustable resistor 335, and contact 336associated with keyboard lever 301. Operation of lever 301 thereforeenergizes solenoid 322 subsequent to closure of pitch contacts 300.

Shaft 308 also has fixed thereto a conducting disc 323 straddled by thepoles of electromagnet 324 having winding 32 5. Winding 325 is connectedin series with battery 326 and adjustable resistor 327. Resistor 327 isadjustable through movement of contactor 328 which is controlled by footpedal 329. It will thus be seen that the speed of rotation of shaft 308and contact 307 is controlled by the position of foot-pedal 329.

Also connected in the dynamic potentiometer circuit are series resistors305, each of which is shunted when a corresponding contact spring 338makes contact with bar 339. The face of bar 339 engaging springs 338 istapered so that the springs are engaged in succession. Bar 339 is fixedto keyboard lever 301 and when lever 301 is depressed, bar 339 is raisedto successively contact springs 338 and shunt resistors 305 successivelyout moved in the way of the dynamic potentiometer circuit, allowingincreasing amounts of current to flow in that circuit. Resistor 305'similar in construction to resistor 305 but associated with a differentkeyboard lever is shown schematically. It will be understood that eachof these resistors or parallel ones extending from lines 303 are alsooperative keyboard levers which are octaves of this note on the mainkeyboard.

Dynamic potentiometer 304' Potentiometer 304' is similar in constructionto potentiometer 304 but is associated. with a diiferent distributorcontact 181 and its associated keyboard levers, representing one noteand its octaves on the main keyboard. Potentiometer 304 has contact307', arm 312', and stops 314' and 320' corresponding to elements 307,312, 314 and 320 of potentiometer 304.

Contact 307 of potentiometer 304 is connected through shaft 308 whichhas ends of insulating material and contact 342 to the contacts of theother corresponding potentiometers, such as contact 307 of potentiometer304' and selector switch 348 to the cathode of triode 350, the plate ofwhich is connected to the control grid of cathode ray tube whichcontains the sine-wave patterns as seen in Fig. 6. Details of theselector switch stop mechanism will be described later under Fig. 9.There will be thirteen attack-decay potentiometers, such aspotentiometers 304304, one for each contact 181 of distributor tube 182,to give one attack-decay characteristic.

Other sets of such dynamic potentiometers not shown having differentattack-decay characteristics may be provided and any set may be selectedby means of switches 348. One stop of switch 348 might bring intooperation a set of potentiometers giving the attack-decaycharacteristics of a piano while another stop might give theattack-decay characteristics of a banjo. The other stops similarlyrepresent other attack-decay characteristics. Each set of attack-decaypotentiometers operated by one stop of switch 348 contains onepotentiometer such as potentiometers 304 and 304' for each contact 181of distributor tube 182. The volume resistors such as 305 of eachkeyboard lever are connected in parallel with each of the associatedattack-decay potentiometers. Such a connection is indicated by wires303. The potentiometers of each attack-decay set are connected to acorresponding contact 181 of distributor tube 182. Such connections areshown at 310.

Inoperation of the circuit shown in Fig. 7, when keyboard lever 301 ispressed, contact 300 is made connecting the grid of pentode 60 with thepitch potentiometer corresponding to lever 301 andcausing a note to besounded by loudspeakers 276 277 (see Fig. 6) said note having apitchcorresponding to lever 301 as explained above. As lever 301 is depressedfurther, contact 336 is closed energizing solenoid 322 and causingcontact 307 of potentiometer 304 to rotate degrees at a speed controlledby the position of foot pedal 329. As the varying voltage picked up bycontact 307 is applied to the grid of triode 350 to control theintensity of the beam in tube 150, the volume of the note soundedincreases at a speed determined by pedal 329 and according to a lawdetermined by the taper of resistor 306 to provide the attack desired.

As long as keyboard lever 301 is held down, arm 312 is held by stop 320and the note is maintained at constant volume in respect to the controlby potentiometer 304 although the volume may be varied by other means tobe described below. When the keyboard lever 301 is releasedsufiiciently, contact 336 is disengaged and solenoid 322 is deenergized.This allows contact 307 to complete its revolution and decrease theintensity of the electron beam in tube 150 to diminish the volume of thenote according to the taper of the resistor 306 and the position of footpedal 329 to provide the desired decay.

The volume of each note may be controlled separately is shownschematically.

by the pressure applied to the corresponding keyboard lever. The amountof pressure applied to lever 301 results in more or less depression ofthe lever against the tension of spring 302. The greater the depressionof lever 301, the more resistors 305 are cut out of the dynamicpotentiometer circuit resulting in a greater amount of current flowingin the circuit and causing a greater intensity of the electron beam intube 150 and a. greater volume of sound. The function of switch 390which is operated by keyboard lever 301 will be described below withrespect to Fig. 9.

It will be understood that it might be desirable in some music that theduration of the decay of a note extend until a time after the finger hasbeen lifted from the keyboard lever. Furthermore the keyboard levers 301could be arranged with a slight purposeful misalignment of key levercontact position so that chords will automatically be played withslightly different initiation times and decay periods in order that atoo mechanical effect be avoided.

A tremolo effect may be produced directly by rapidly varying thepressure on each keyboard lever since volume is a function of the amountby which the lever is pressed. However, a more sustained effect may beproduced by the means shown in Figs. 2 and 2a. A light source 580produces light which is directed into a beam 589 by optical element 581.The light beam 589 is focused by optical element 582 on the cathode ofphotosensitive cell 583. Directly adjacent light beam 589 are aplurality of reed elements 584. Each reed element 584 as seen in Fig. 2aconsists of a thin reed 586 anchored at one end to the frame of themusical instrument. The other end carries an obturating means 588 andhandle means 587. Photocell 583 controls the grid of a tube in theamplification circuit.

In operation, when a sustained automatic tremolo effect is desired, themusician displaces one of reeds 584 by pressing and rapidly releasinghandle 587. The reed will then continue to vibrate, alternatelyblocking, or partially blocking, light beam 589 from photocell 583 andcausing the volume of the music to vary rapidly in volume in accordancewith the period of vibration of the reed caused to oscillate. The reeds584 are each of different length or thickness so that each will vibrateat a different frequency. The reeds may be made to vibrate singly or inany desired combination. Electromagnetic driving means may be arrangedfor causing the reeds to continuously vibrate. This means for producingautomatically a tremolo effect is preferably placed closely behind thekeyboard as shown in Fig. 2 for the convenience of the musician. It willbe obvious that such a tremolo producing means could be used with eachmanual for individual results or even with each harmonic of a note.

In Fig. 8 is shown over-all volume potentiometer 252 also shown in Fig.6. The adjustment of potentiometer 252 is controlled by foot pedal 360.The position of foot pedal 360 therefore controls the over-all volume ofthe instrument.

There being a dynamic potentiometer circuit corresponding to the onecontaining potentiometer 304 associated through switch 343 with eachcontact 181 of tube 182, the action of distributor tube 182 is to causethe electron beam of tube 150 to be modulated successively during smallincrements of time in accordance with the keyboard levers operated, theproper attack or decay volume being impressed on each note as it issounded during its increment of time.

Reference is now made more particularly to Fig. 9 for a description of aquality control circuit used in this invention. Tube 150, patterns156165, and compensating resistors 225 correspond to those elementsshown in Fig. 6. Resistors 225 are each connected to a contact spring375. Opposing contact springs 376 are connected to ground. Betweencontacts 375 and 376 are intermediate contact springs 377 each havingfixed thereto a downwardly extending projection 378 of insulatingmaterial. Springs 377 are normally in contact with springs 376.Intermediate springs 377 may each be connected through switches 379 toharmonic attenuator resistors 226. Alternately switches 379 may connectselected harmonic patterns to ground eliminating the harmonics soconnected.

Immediately above the top intermediate spring 377 is the end of aplunger 384 fixed to the core of solenoid 385. The plunger 384 is biasedupwardly by spring 386 and extends through dashpot 387, the action ofwhich is regulated by handle 388. Solenoid 335 is connected in serieswith battery 392 through contact 390 of keyboard lever 301.

When keyboard lever 301 is depressed, it will be seen that solenoid 385will be energized by the closing of contact 390. Operation of solenoid385 will urge shaft 384 downward against the tension of spring 386 at aspeed determined by dashpot 387 and the setting of regulating handle388. As shaft 334 progresses downwardly, first spring 377 will disengagespring 376 and engage spring 375, thus disconnecting fundamental pattern156 from ground and connecting it in the parallel circuits of harmonicresistors 226 and 226 or 226".

As shaft 384 moves further down the second spring 377 is moved todisconnect the second harmonic pattern 157 from ground and connect it inthe potentiometer circuit of resistors 226, 226' or 226 associated withthe second harmonic. The remaining harmonics are thus added to theaudible note in rapid succession.

Paterns 156165 may be connected through resistors 225, contact springs375-377, switches 379, through harmonic attenuators 226 and 226connected in parallel, through battery 392 and the electron beam of tubeto form a complete potentiometer circuit. Sliding contacts 393 are fixedto rods 394- moved against a restraining spring, not shown, by floatingbars 395 which in turn are moved by cams 396. Cams 396 are mounted onshaft 397 which is turned by rack and pinion 398. The rack is fixed tostop 399.

Movement of stop 399 to various positions will be seen to suppress oraccentuate the various harmonics as deter mined by the shapes of thecams 396. When resistors 226 control quality, there may be simulatedquality within one tone classification, i.e. Woodwinds, while move mentof stop 399 may produce variation within that classification, such asoboe, clarinet, etc.

Each resistor 226 is mounted on a resistor support 402 which is slidablewith respect to contact 393 as determined by the position to stop 40-3.A spring tensioned ball 404 fitting in a notch on shaft 405 of stop 403allows the operator of the instrument to know by touch when the stop isin its normal position. Stops 403 allow each harmonic to be separatelyadjusted.

Alternate harmonic attenuator resistors 226' have con tacts 393 moved byshafts 394. Shafts 394' are moved by floating bars 395 againstrestraining springs, not shown, which are in turn moved by cams 396'.Each cam 396 is rotated by a shaft 397 and each shaft 397' is rotated bya separate knob 408. Thus the attenuation of each harmonic may bepre-adjusted or pre-set to a degree, before starting a rendition chosenby the musician. Cams 296 aid in keeping contact 393 at the selectedposition and allow the contact 393 to have a different motion from thatof knobs 408.

A third set of alternate harmonic resistors 226" are provided. Theseresistors are for independent separate harmonic control and areconnected to stops in the form of calibrated sliding handles or tolevers for rapid manipulation. They are not intended for group action.Resistors 226" are always connected and are intended for rapidmanipulation to achieve variations in the quality already set in theinstrument by the musician.

Switch 410, at the operation of the musician, selectively connects thecontacts of the potentiometers containing resistors 226, or 226' to thepulse integrator and thus causes the notes sounded to be in accordancewith the harmonic-attenuation determined by the harmonic-attenuatorgroup selected. It will be understood that there would be a number ofsets of resistors such as 226 representing tone families such as theoboe, clarinet, etc., and that there could be a number of sets ofresistors such as 226 at the command of the musician.

Switch 410 includes curved clamps 411 having opposed concave curves,said clamps being urged together under tension to have .oppositeparallel motion when forcibly separated. Buttons 412 are urged upwardlyby springs 413 and have lower bulbous portions 414 adapted to besqueezed between clamps 411. As one button 412 is pressed down and theassociated bulbous portion 414 squeezes clamps 411 apart, the bulbousportion already between clamps 411 will escape, forced up by its spring413. Switch 410 operates to connect one set of contacts 393 or 393 tothe pulse integrator and thus allows selection by the musician to thetype of quality control used. This selector device would also beadaptable for use with dynamic selector switch stop 348 of Fig. 7.Switches such as 390 are operated by other keyboard levers.

In Fig. 10 is shown an alternate form of quality control employingcapacity attenuation. As explained by Figs. SCI-f, the beam current isin the form of high frequency pulses which may be attenuated bycapacitance. In Fig. patterns such as 156 are each connected to aresistor 227, all of which are connected through overall attenuationcondenser 421, coupling circuit pulse integrator, detector 420 andamplifier 237, these elements being similar in function to elements 128,129, 135, and 136 of Fig. 4, and loud speaker 276. Voltage is appliedbetween anode patterns 156 and cathode of the cathode ray tube bybattery 422. The various attenuating bleeder circuits, condensers 421,423, 425 and 425' discharge between pulses except 421, which dischargesdirectly, through resistors 22 7 and battery 422 .to cathode. Othertypes of impedance, either variable resistors or inductors, may replacethe condensers shown here.

In the modification of Fig. 10, frequency compensation for the naturalcharacteristics of the ear is accomplished by condensers 423 which varythe voltage at the junctions-of the. patterns such as 156 and resistors227.

In parallel with condensers 423 areharmonic-attenuator condensers 425,one condenser 425 being connected between each pattern, such as 15.6 andth lectro beam potential supply. Condensers 425 provide tone familiessimilar in function to stop 399 of Fig. 9 and 425 for use similar tostop 408 or resistors 226' (Fig. 9 that is for pre-set qualities orindependent control. Switches 424 permit alternate selection of thesystem including condensers 425 or the system including condensers .425.Condensers 425 comprise .a relatively movable plate, or plates, 426 and.a relatively fixed plate, or plates, .427. Movable plates 426 are shownto be mounted on shaft 434 for rotation. Shaft 434 has mounted thereon apinion 431 which is rotated by oppositely acting stops 429 and 430 eachof .which carries a rack meshing with an oppositeside of pinion 43,1.Plates 426 can therefore be rotated to any desired degree by pushing oneor the other of stops 429-43,0. Plates 42 6 and 427 are shapedtoa-ttenuate the various harmonics to achieve the sound effects desiredfor the various settings of stops 429430.

Relatively fixed plates 427 .may also be separately rotated with respectto plates 426 by stops 428 carrying racks meshing with pinions Jfixed toplates 427. Stops 428 allow individual adjustment of the attenuation ofthe various harmonics .within the tone family compass asdesired by themusician.

In .Fig. 1.1 is shown antalternatively distributor-switch arrangement inwhich .a plurality of gas filled tubes such as tubes 435, .436, .437,and 438, each have .an anode, control grid, and cathode. Each of thecathodes of tubes 435-438 is connected to a common junction point 445through a variable cathode resistor 440 and a potentiom eter 441. Theanodes of tubes 435-438 are connected together through conductor 446 andto the cathode through common junction point 445 and battery 447.Cathodes of adjacent tubes 435-438 in the ring-like series are connectedthrough condensers 442. The grid of each tube 435-438 is connected tothe cathode of the preceding tube in the series by resistors 448 and449, and battery 450. Voltage taps on potentiometers 441 are connectedto the grid of pentode 60 which corresponds to pentode 60 in Fig. 6.Switches 439' between the taps on potentiometers 441 and the grid oftube 60 constitute keyboard lever switches corresponding 300 and 300 ofFig. 7.

Relaxation generator 452 of conventional construction generates asuccession of positive pulses of steep wave front at supersonicdistributor frequency. The interval between pulses is the increment oftime during which one note will be sounded until it is reached again byoperation of the distributor circuits The pulses generated byoscillator452 are applied to the grids of tubes 435-438 throughcondensers 453. It will be understood that in the actual circuit usedthere will be thirteen gaseous triodes such as tubes 435-438, onecorresponding to each of the electrodes 181 in tube 182 of Fig. 7.

In explaining the operation of the circuit of Fig. 11, it will beassumed that tube 435 is conducting. Since tube 435 is conducting,current is flowing through resistor 440 connected with the cathode ofthat tube and hence the negative bias on the grid of tube 436 is loweredbecause of the connection through resistors 448 and 449 and battery 450to resistor 440. Batteries such as 450 are for the purpose ofmaintaining a negative bias on the grids of, tubes 435-438. When thenext positive pulse from relaxation oscillator 452 is applied to all thegrids of tubes 435-438, tube 436 will begin to conduct since it has asufficiently low grid bias. Tubes 437 and 438 do not have a sufficientlylow grid bias to be rendered conducting by the pulse. When tube 436begins to conduct the drop across its resistor 440 charges the condenserbetween the cathodes of tu'bes 435 and 436 making the cathode of tube435 so positive that the tube stops conducting. On arrival of the nextpulse from oscillator 452 tube 437 will begin to conduct and tube 436will be cut ofi. This process is continuously repeated, each pulse fromoscillator 452 causing the next tube to con- .duct and the tubepresently conducting to :be cut off. Similar circuits employing vacuumtubes are known to the art and may be employed in place of the gasfilled tube circuit shown.

Reference is now made more particularly to Figs. 12 and 13 for adescription of an embodiment of this invention using continuous harmonicpatterns. In this embodiment cathode ray tube 490' which includeshorizontal and vertical deflection plates 491 and 492, respectively,carries on its end wall 493 and concentric therewith a plurality ofring-like, substantially flat, continuous patterns 494, the radialdimensions of which vary in sinusoidal manner. The innermost of patterns494 varies in radial dimension as a single complete sine wave. Theadjacent pattern varies to form two complete sine waves and thesucceeding patterns similarly form the successively higher harmonics.

Patterns 494 are ,each connected to the harmonic compensation andattenuation circuit 498 which is in turn connected through pulseintegrator circuit 237, detector 244 and amplifier 260 to speaker 276.Harmonic compensation andattenuation circuit 498 contains compensationand attenuation resistors 225 and 226 shown in Fig. 6. Circuits 237,244, and 26,0, and speaker 276 have a similar construction and operationto that of the same numbered circuits in Fig. 6. Frequency-controlcircuit 501 contains tube 60andits associated circuit shown in Figs. ,1,and ,6. Distributor 502 contains and electronic dis- :tributortubesirn'ilar to tube 1820f Fig. 6. Keyboard 500 is interconnected withfrequency control circuit 501 and distributor circuit 502, so that thereis produced in the output of frequency control circuit 501 a voltagehaving a magnitude indicative of the pitch of the note being played onkeyboard 500 and sounded at that increment of time. Distributor 502operates to cause the output voltage of frequency control circuit 501 tosuccessively represent over small increments of time the various notesplayed on keyboard G0.

Sine wave oscillator 503 produces a sine wave of a frequency controlledby the output voltage of frequency control 501. Such circuits formodulating frequency are well known. The sine wave produced by circuit503 is split into two sine waves 90 degrees apart in phase but eachhaving the frequency of the original sine wave. The splitting of theoutput of circuit 503 is accomplished by the circuit including condenser505 and resistor 506. One of the quadrature sine waves is applied tohorizontal sweep circuit 507 through transformer 508 while the otherquadrature sine Wave is applied to vertical sweep circuit 509 throughtransformer 110. Vertical and horizontal sweep circuits 507 and 509 aremodulator circuits which modulate the amplitude of the voltages appliedto the input circuits thereof. This amplitude modulation is controlledby saw-tooth oscillator 515 which is a circuit capable of generating asaw-tooth wave having a frequency relatively high compared to thefrequency of sine wave oscillator 503. The saw-tooth wave produced byoscillator 515 is applied to sweep circuits 507 and 569 to modulate inamplitude the quadrature waves from circuit 595 and 506. The deflectionwaves produced by horizontal sweep circuit 507 and vertical sweepcircuit 509 are applied to horizontal deflection plates 491 and verticaldeflection plates 492, respectively, of tube 490.

Saw-tooth oscillator 515 is connected to pulse integrator 237 throughpeaker circuit 516 which is constructed similarly to peaker circuit 246in Fig. 6 and operates to derive a pulse from the radial returndeflection voltage of the saw-tooth wave developed by circuit 515. Thepulse from peaker 516 trips integrator 237, discharging the condensertherein as explained above.

In the operation of the embodiment of the invention shown in Fig. 12,keyboard 500, distributor 502, and frequency control circuit 501 act toproduce a series of voltages, each representing the pitch of thekeyboard lever depressed and each lasting over an increment in asupersonic distribution period as explained above. Each short voltagelevel frequency modulates sine wave oscillator 503 to produce a sinewave having a frequency indicative of the pitch of the keyboard leverproducing said voltage level.

The two quadrature voltages produced by circuit 505 506, having afrequency as produced by sine wave oscillator 503, cause the pencil beamproduced by tube 490 to describe a circular trace on the end wall 493.Sawtooth oscillator 515 modulates the amplitude of the verticaldeflection voltage causing the circular trace on end wall 493 to becontracted and expanded over the patterns 494 at a high rate of speed.This results in a rapid radial scan which moves circumferentially overpatterns 494 at a rate determined by the note played on keyboard 506that momentarily is being sounded by the instrument through the actionof distributor 502.

The signal produced by patterns 493 passes through circuits 498, 237,244, and 260 where it is handled in the same manner as described in Fig.6. Peaker 516 operates to trip pulse integrator 237 and add the signalsproduced in one radial sweep by the electron beam of tube 490 also asexplained in regard to Fig. 6. Speaker 276 produces the audibleoscillations.

Another embodiment of part of this invention is. shown in Figs. 14 and15 in which the sine wave patterns 530 have a cylindrical or conicalsurface and are placed inside of the cylindrical or conical envelope ofvacuum tube 531. Patterns 530 may be mounted on a separate cylindricalmounting member as shown in Fig. 15 or mounted directly on the innersurface of the envelope of vacuum tube 531. Tube 531 also has a centralaxial cathode 532. The patterns 530 are each connected to theattenuation circuits 40 which are in turn connected through amplifier 42to speaker 43. The deflection circuit for rotating the electron beamproduced in tube 531 by cathode 532 is not shown in Fig. 14.

Fig. 15 shows an end view of tube 531 without the connection to thepatterns 530 but with deflection coils 535, 536, 537, and 533, each ofwhich extends the length of tube 531. Opposite coils 536 and 538 areconnected in series to oscillator 542 through transformer 543. Oppositecoils 535 and 537 are connected in series with condenser 539 and inparallel with coils 536 and 538 through transformer 543 to oscillator542.

The tank circuit for oscillator 542 consists of condenser 543 and one ofcoils 544, each of which is connected to one of the thirteen electrodes547 arranged in a circle on the end wall of cathode ray distributor tube549. The electron beam of tube 549 is caused to sweep in a circle overelectrodes 547 by sweep circuit 548 which impresses quadrature sinewaves on the deflection plates of tube 549. The tank circuit abovedescribed is coupled to oscillator 542 by condensers 551 and 552.Battery 550 supplies the cathode-anode potential necessary to producethe electron beam in tube 549. The oscillatory current produced byoscillator 542 is prevent from passing through battery 550 by choke coil545. Twelve of the coils 544 each represent one note of an octave andhave a series of switches 555 one for each octave of the main keyboardsuch as keyboard of Fig. 2. The thirteenth electrode 547 is connected toa coil having a switch 555 for each keyboard lever of octave keyboardsuch as 66 in Fig. 2, each switch 555 being operated by a keyboardlever, each coil 544 is connected to oscillator 542 through a switch 546arranged to be closed along with the closing of any switch 555associated with the said coil 544. All of switches 555 and coils 544 arenot shown.

In operation of the system shown in Figs. 14 and 15, when no keyboardlever is pressed and no switch 555 is closed, the characteristics ofoscillator 542 are such that it does not oscillate. However, when aswitch 555 is closed along with the closing of its corresponding switch546, through operation of a keyboard lever, oscillator 542 oscillateswhen the beam of tube 549 impinges on the corresponding electrode 547,and this oscillation is determined by the amount of coil 544 shorted outand this depends on the pitch represented by the keyboard leverdepressed.

The sine wave developed by oscillator 542 is split into two quadraturewaves by action of condenser 539. These quadrature currents applied tocoils 535, 536, 537 and 538 cause the sheet-like electron beam developedby cathode 532 to rotate and sweep over patterns 530 at a rate of speeddetermined by the instant frequency of oscillator 542 and in turn by thekeyboard lever pressed. It will be understood that the magnetic fieldsset up by deflection coils 535-538 not only rotate the electron beam oftube 531 but are also effective in forming the electrons from cathode532 into a sheet-like beam.

The signals generated by patterns 530 as the electron beam sweeps overthe varying surface of said patterns is altered by attenuator circuitsto achieve the desired quality and amplified and rendered audible all asdescribed with respect to Fig. 1. It will be understood that when aplurality of keyboard levers are pressed simultaneously closing a switch555 on each of a plurality of coils 544, that the corresponding notesare sounded successively at a super-audible rate also as described withrespect to Fig. 1. It is to be understood that, if space permits, all ofthe notes and their harmonics may be represented by patterns and nosuper-audible switching device employed or that other combinations ofpatterns be used than here described or that octaves be obtained bydoubling circuits.

Reference is now made to Figs. 16, 17, and 18 for a description of analternative embodiment of the discontinuous sine patterns in whichcomplementary patterns are used .connected in push-pull relation.Cathode ray .tube 560, of the type which generates a pencil-like beam,carries on its end wall a plurality of sine wave patterns designatedgenerally as 561.

These patterns are shown more particularly in Figs. 17 and 18 the latterfigure showing a side view. Sine wave patterns 562 and 563, representinga fundamental wave, are complementary and 180 degrees out of phase.Patterns 562 and 563 are mounted in close proximity, but not in contactwith each other on insulating member 568, which may be the end wall oftube 560. It will be understood that patterns 562-565 are mounted insidethe tube 560 for impingement thereon by its electron beam. The secondharmonic is represented by complementary patterns 564-565 also 180degrees out of phase. Although these patterns of Figs. 17 and 18 areshown of the discontinuous type the principal is also applicable to thecontinuous forms shown in Figs. 12 and 14. It will also be understoodthat the deflect-ion means associated with cathode-ray tube 560 in Fig.16 are connected to suitable deflecting circuits in the same manner asillustrated in Fig. 4, for example, by means of the leads 117a, 118a.

One of each pair of patterns is connected through attenuator circuits570 and integrator and detector circuits 571 to the grid of tube 572, anamplifier tube connected in push-pull relation with amplifier tube 577through transformer 579. Transformer 579 is connected to speaker 43. Theother of each pair of patterns is connected through attenuator circuits575 and integrator :and detector circuits 576 to the grid of amplifiertube 577. Attenuator circuits 570 and 575 contain harmonic compensatorresistors and harmonic attenuator resistors corresponding to resistors225 and 226, respectively, of Fig. 6. Integrator and detector circuits571 and 576 contain circuits 233, 237, 244, 253, and 256 of Fig. 6.

In the operation of the embodiment shown in Figs. '16, 17, and 18 thepencil beam of tube 560 is caused to be deflected horizontallysuccessively across the patterns at a speed determined by the pitch ofthe keyboard lever pressed as explained with respect to Fig. 6. The beamof tube 569 is also deflected vertically at a relatively high rate alsoas in the embodiment of Fig. 6. The signals produced by the two sets ofpatterns are 180 degrees out of phase. These two signals are attenuated,integrated and detected as explained with regard to Fig. 6 and areapplied in push-pull relation through tubes 572 and 577, and throughtransformer 579 to speaker 43.

The sinusoidal patterns representing the fundamental frequency and theharmonics may be made, as described above, by attaching thin metal foilto the end wall of the cathode ray tube or on a separate insulatedmountv ing plate. These patterns may be made by photo- .engravingprocesses from a master plate which has been photographed from anenlarged drawing. The patterns may alternatively be sputtered on theinsulated mounting plate through a master template or the whole surfacesputtered, then covered with a rubber-like anodically formed background,sand blasted and the rubber removed. Another possibility of producingthese patterns would be by forming them on-an aluminum plate by an .ink,known to those skilled in the art, which resists anodizing. The platewould then be anodized, leaving a non-conducting oxide on the surfaceexcept on the inked portion. The ink can then be dissolved leaving.sinusoidally shaped aluminum conducting surfaces surrounded by anon-conducting oxide surface.

Another alternate anode construction could be availed .of in which thereis a conducting plate having sinusoidally shaped holes representing thefundamental and harmonics. Behind each sinusoidally shaped hole, withIespect to the electron gun, would be a separate conducting plate at ahigh positive potential. The front plate 22 having the sinusoidallyshaped holes is at a relatively low potential.

The focusing and deflecting of the electron beam in the cathode ray tubecontaining the patterns may be done by electromagnetic means orelectrostatic means or by a combination of electromagnetic andelectrostatic means. The form of the anode current fluctuations isdetermined, as previously explained, by the shape of the anode patternsand the rate of deflection of the electron beam. Consequently patternshape and sweep characteristics cannot be considered separately. If aknown tone quality is to be synthesized, said tone having been analyzedinto its elemental sinusoidal vibration components according to Fouriersmethod, then patterns of sine wave form would be required, assuming thatthe horizontal or X axis deflection is linear. Shapes of anode patternscompensated for non-linearity have been treated in Patent 2,075,802. Forthe purpose of developing a new tone quality the generated sound waveform originating from each pattern and transmitted to the ear should besuch that the sensory response of the ear is itself elemental.

The mounting plate on which the patterns are mount ed is preferably ofglass, mica or other substance which will withstand outgassing of thetube. Intercapacity coupling between adjacent patterns may be reduced byusing separate plates for each wave pattern and mounting them in a frameeach at an agnle to the other like the slats in a Venetian blind whenpartially opened. Although the patternsin Figs. 1, 4, 6, 9, 16, and 17have been shown flat, it will be understood that in actual practice itis preferable that these patterns present a spherical surface to theelectron beam impinging thereon. It may also be advantageous to placecontrol grids in front of the anode patterns and relatively adjacentthereto for control purposes. Grids or other collecting electrodes mayalso be placed near the patterns to collect secondary electron emissionfrom said patterns and thus derive the anode signal by secondaryemission rather than by a direct action of the electron beam upon theanode patterns.

Since the patterns are symmetrical along the horizontal axis a circuitwhich would supply a Wave form with a uniformly slow rise and fall tothe horizontal deflecting plates would serve as well as a sawtooth wavehaving relatively slow rise and relatively rapid fall. This defleetingvoltage would have the wave form of an isosceles triangle and is knownas a back to back wave form. A voltage wave of this shape may begenerated by methods known to the art including the combination of asine wave oscillator followed by a squaring circuit and finally by anintegration stage employing a time constant about ten times that of theperiod of the cycle. Amplification would then be required before thevoltage could be applied to the deflection plates. The integratorconsists of a potential divider made up of a condenser and resistor inseries. The integrated output voltage is derived from the condenserterminals. A trapezoidal voltage wave form may be generated for usewhere magnetic deflection is employed, as is employed in some types oftelevision scanning.

It is to be noted that it will be possible to simultaneously sound twodifferent dynamic effects as well as two different qualities on aZ-manual instrument having .two complete keyboard systems as shown inFig. 2, each of said manuals being associated with a system containingordinary patterns as shown in Fig. 6. If push-pull patterns are used asshown in Figs. 16, 17, and 18 .one manual .can control the soundsproduced by one anode of each pair of the push-pull patterns thuspermitting the use of one cathode ray tube with two manuals. If a singlemanual is associated with a cathode ray tube containing push-pullpatterns the wave derived from each set of patterns may be differentlycontrolled as to dynamic and qualitative characteristics sothattwenty-six different

